This is a continuation of application Ser. No. 10/215,096 filed on Aug. 8, 2002, now abandoned.
1. Field of the Invention
The present relates to the removal of acetylenic compounds from olefin containing streams, in particular streams containing diolefins.
2. Related information
The crude streams for the commercial production of olefins and dienes contain various compounds as impurities. Acetylenic impurities need to be removed from the streams to produce acceptable quality olefin and diene products. A preferred technique for removing the acetylenic impurities is partial hydrogenation, often called selective hydrogenation. For the commercial production of olefins and dienes, the catalytic hydrogenation of acetylenic compounds is utilized to remove acetylenic impurities in the crude product stream.
To produce olefins such as ethylene, propylene, butadiene, isoprene and the like, acetylenic impurities such as acetylene, methyl acetylene, vinyl acetylene, ethyl acetylene, 2-methyl-1-buten-3-yne and the like, in various crude mixed C2-C5 streams need to be removed with minimum loss of useful materials such as ethylene, propylene, butenes, butadiene, isoprene and the like in the feed streams. The preferred technique for the purification in commercial practice is the selective hydrogenation of acetylenic compounds over hydrogenation catalysts.
The difficulty in the catalytic hydrogenation of acetylenic compounds rises from the fact that the hydrogenation must be carried out in the presence of a large excess of olefins or dienes or both. Under the industrial conditions, valuable olefin and diene products in the crude product streams are not inert. This is especially true as the conversion of acetylenic compounds approaches completion, resulting in the loss of valuable products. Therefore, during the selective hydrogenation of acetylenic compounds, minimizing the loss of olefins and dienes is highly desirable for the commercial production of olefins such as ethylene, propylene, and styrene and dienes such as 1,3-butadiene and isoprene. The selectivity of a catalyst is often the determining factor in selecting a catalyst for the production of olefins and dienes.
Acetylenic compounds have been hydrogenated over all Group VIII metals and copper catalysts. Specifically catalytic partial hydrogenation of acetylenic compounds to olefinic compounds which are important for industrial production of olefins, dienes and fine chemicals. All Group VIII metals (Pd, Pt, Rh, Ru, Ir and Os) and non noble metals (Fe, Co and Ni), and Cu catalysts have been known to be active for the hydrogenation of acetylenic compounds and olefins. All Group VIII noble metal catalysts and Ni catalysts have satisfactory catalytic activities for application in the commercial hydrogenation process. But more important for a catalyst is the selectivity for the hydrogenation of acetylenic compounds because of over hydrogenation of olefinic compounds during hydrogenation of acetylenic compounds.
The difficulty of hydrogenating an acetylenic group in a molecule depends on the location of the triple bond on the molecule whether there is conjugation or an olefin group. An isolated terminal triple bond is easiest to selectively hydrogenate. Conjugated triple bond with double bond is much more difficult for the selective hydrogenation. In the study on the hydrogenation of acetylene, methyl acetylene, and dimethyl acetylene (G. C. Bond et al., J. Catalysis 174, 1962), it is reported that the order of decreasing selectivity is Pd>Rh>Pt>Ru>Os>Ir. L. Kh. Freidlin et al., Dokl. Akad. Nauk SSSR 152 (6), 1383, 1962 reported that the order is palladium black>platinum black>rhodium black>Raney nickel>Raney cobalt for the terminal acetylenes and palladium black>Raney nickel>platinum black>Raney cobalt>rhodium black for internal acetylenes. Palladium on barium sulfate is reported to be more selective than Raney nickel in hydrogenation of vinyl acetylene in liquid phase (Catalytic Hydrogenation over Platinum Metals by Paul. N. Rylander, p.75, Academic Press, 1967). Product analysis at 100% conversion of vinyl acetylene indicates that the product from Raney nickel catalyst contains only about half the butadiene (35%) and 23 times the butane (23%) compared with the product from palladium supported on barium sulfate.
Supported Pd, Ni, Cu and Co catalysts have been known to be useful for the hydrogenation of acetylenes (Handbook of Commercial Catalysts, pp. 105-138, Howard F. Rase, CRC Press, 2000). The most preferred catalysts in commercial application of selective hydrogenation of acetylenes are palladium-based catalysts such as Pd, Pd/Pb, Pd/Ag or Pd/Au on a support such as alumina and the copper catalyst on a support such as alumina. Pd catalysts are the most preferred catalysts because of high activity and supposedly superior selectivity compared with other metal catalysts.
The prior art widely demonstrates that palladium catalysts have the highest selectivity for the selective hydrogenation of acetylenes among Group VIII metals. No art has been found showing higher selectivity of nickel catalysts over palladium catalysts. In fact, palladium catalysts are the choice of all current commercial processes for the selective hydrogenation of acetylenic impurities (vinyl acetylene, ethyl acetylene and methyl acetylene) in the crude butadiene streams and crude C3 olefin streams.
1,3-Butadiene is an important raw material for production of various polymers such as butadiene-styrene copolymer. One of the processes for producing 1,3-butadiene is co-production of various olefins by steam cracking of petroleum fractions. The crude mixed C4 stream from a steam cracker is selectively hydrogenated to partially remove C4 acetylenic compounds. The selectively hydrogenated stream is sent to the 1,3-butadiene recovery unit where solvent extractive distillation is used to separate 1,3-butadiene from the rest of components in the mixed stream. Complete removal of C4 acetylenic compounds in the stream with high recovery of 1,3-butadiene is highly desirable to reduce the production cost of 1,3-butadiene and produce premium quality product for polymer production. Heretofore, it was technically impossible to completely remove C4 acetylenes in crude mixed streams by selective hydrogenation without an unacceptably high loss of 1,3-butadiene due to over hydrogenation of 1,3-butadiene. Therefore, an improved inexpensive process via highly active and selective catalysts is highly desirable to produce premium quality 1,3-butadiene without paying a penalty for high loss of 1,3-butadiene due to over hydrogenation.
The palladium-based catalysts for selective hydrogenation of C4 acetylenic compounds are highly active. However, their level of selectivity does not allow complete removal of C4 acetylenes without an unacceptable high loss of 1,3-butadiene due to over hydrogenation. Another inherent problem of palladium-based catalysts is the loss and migration of palladium due to the formation of soluble Pd complex compound by the reaction of Pd atoms on the catalyst surface with vinyl acetylene, if the hydrogenation is carried out in the presence of a liquid phase. Silver and gold have been used to minimize the loss of palladium and reduce catalytic polymerization of acetylenic compounds. Palladium-based catalysts are disclosed in U.S. Pat. No. 5,877,363 (1999), and EP 0 089 252 (1983). U.S. Pat. No. 5,877,363 (1999) disclosed the process for the selective hydrogenation of acetylenic impurities and 1,2-butadiene in mixed olefin rich C4 streams by using supported Pt and Pd catalysts.
The copper-based catalyst is very selective so that the recovery of 1,3-butadiene from the mixed stream is higher than palladium-based catalysts. However, since the activity of copper catalysts is very low compared with palladium-based catalysts, a large volume of catalyst and large reactor are required. The copper catalyst cokes up quickly and frequent regeneration of the catalyst is necessary. Such catalysts are disclosed in U.S. Pat. No. 4,440,956 (1984) and U.S. Pat. No. 4,494,906 (1985).
In the present research it was found that the selective hydrogenation of C3 and C4 acetylenic compounds in a crude butadiene stream over a supported commercial Pd (0.2 wt. %)-Ag (0.1 wt. %) catalyst decreases as the hydrogenation temperature increases; an effect also noted by H. Uygur et al. in liquid phase selective hydrogenation of methyl acetylene/propadiene (MAPD) in a mixed C3 stream (J. Chem. Eng. Japan, 31, p. 178, 1998). This seemingly strange behavior is attributed to a combined effect of very low activation energy (<0.5 kcal.mole) of the selective hydrogenation in liquid phase, higher hydrogen solubility in the feed stream at lower temperature, and temperature dependency of adsorption of acetylenic compounds on palladium surface in ternary phase reaction system of gas, liquid and solid catalyst. The concentration of hydrogen in the liquid phase is more influential on the selective hydrogenation rate of acetylenic compounds than the effect of activation energy.
According to R. S. Mann et al. (Can. J. Chem. 46, p. 623, 1968), Ni and Ni—Cu alloy catalysts are effective for methyl acetylene hydrogenation. The catalytic activity rapidly increases with addition of copper to nickel up to 25 wt. % in alloy catalyst. The selectivity to propylene and extent of polymerization increase with increasing of copper in the alloy.
According to H. Gutmann and H. Lindlar (Organic Synthesis, Chapter 6), vinyl acetylene and 2-methyl-1-buten-3-yne are difficult to selectively hydrogenate to 1,3-butadiene and isoprene by using the usual palladium, nickel or cobalt catalysts. But the palladium catalyst supported on calcium carbonate treated with mercury acetate is useful for the selective hydrogenation.
Nickel-based catalysts are known in the art to be effective for the selective hydrogenation of acetylenic impurities in mixed streams of olefins. It is well documented that nickel catalysts in any form are highly active for hydrogenation of olefins and benzene. Because of very high activity of Ni catalysts for hydrogenation of olefins, the selective hydrogenation of acetylenes in mixtures of dienes or olefins is preferentially carried out over the presulfided nickel catalyst or in the presence of moderating agent for the nickel catalysts, as known in the prior art.
There is no disclosure of selective hydrogenation of C4 acetylenes in crude butadiene streams in the presence of a supported nickel metal catalyst in unsulfided form as equal or superior to the palladium-based catalyst. Nickel catalysts are disclosed in U.S. Pat. No. 4,504,593 (1985) and U.S. Pat. No. 3,691,248 (1972).
U.S. Pat. No. 4,504,593 teaches the use of supported bimetallic catalyst comprised of at least one group VIII metal selected from the Pt, Pd, Ni and Co group, and at least one metal from the Ge, Sn, and Pb group for selective hydrogenation of acetylenic hydrocarbons and diolefins in the olefinic mixtures to mono-olefins. The catalyst contains 0.1 to 10 wt. % Ni, preferably from 1 to 5 wt. %, on a support such as alumina (70 m2/g and 0.5 cc/g total pore volume). The catalysts are prepared in two steps, introducing the second component (Ge, Sn or Pb) of the catalyst to the Ni catalyst from the first step. The selective hydrogenation is preferably carried out in the presence of sulfur and nitrogen compound to obtain acceptable improved selectivity. However, the patent does not suggest the selective hydrogenation of C4 acetylenes in mixed butadiene streams in the absence of sulfur with the activated Ni metal catalyst.
U.S. Pat. No. 3,793,388 (1974) disclosed the selective hydrogenation of acetylene in olefin mixtures in the presence of nickel catalyst supported on alumina. The alumina is characterized by having a substantial portion of pores having at least 120 Å diameter and at least 2 m2/g surface area. The nickel content on the catalyst is from about 0.5 to about 8 mg per square meter of total alumina surface area.
Br 1,182,929 (1970) disclosed a useful catalyst for selective hydrogenation of acetylenic hydrocarbons in an olefin mixture such as crude butadiene stream. The catalyst is the nickel promoted copper catalyst supported on a carrier. The weight of the copper component on the catalyst exceeds the weight of Ni and the weight of the carrier exceeds the weight of active metal components. The final catalyst in mixed oxide form is prepared by calcining a mixture of oxides at 850° C. The catalyst is activated by reducing at a temperature from 180° to 600° C. with a hydrogen-containing gas. The metallic active components on the activated catalyst is at least 25% by weight of the active metal components. The remaining percentage is in the form of their oxides. The selective hydrogenation is carried out in gas phase at a temperature from 100° to 250° C. and about 1 WHSV. The cycle time is about 420 hours.
U.S. Pat. No. 4,748,290 (1988) disclosed a nickel boride catalyst supported on alumina for hydrogenation of acetylenic and diolefinic compounds to monoolefinic compound. Reacting supported nickel arsenate with a borohydride compound activates the catalyst.
U.S. Pat. No. 4,831,200 (1989) disclosed the process for a two-step selective hydrogenation of acetylenic impurities in crude butadiene stream. The acetylenic impurities in crude feed streams are partially hydrogenated in the palladium-based catalyst disclosed in U.S. Pat. No. 4,533,779 and then the remaining impurities are hydrogenated in the copper-base catalyst disclosed in U.S. Pat. Nos. 4,493,906 and 4,440,956 discussed above.
The present process has as an advantage of a greater selectivity for the removal of acetylenic compounds from hydrocarbon streams with higher yields of the desired olefinic compounds. In particular, the present process provides a higher yield of 1,3-butadiene of higher purity from crude C4 streams. It is a particular feature of the present invention that it employs an inexpensive and readily available catalyst at key points in the process which leads to a further advantage that other sulfur or heavy metal sensitive catalysts such as the palladium and copper-based catalysts may also be employed down stream for further improvements. These and other advantages and features of the present invention will become apparent from the following disclosures.